Every patient at risk for hemorrhage has at least one peripheral intravenous cannula inserted upon admission to the Labor & Delivery Unit. A 2nd IV cannula is almost always placed, usually when the decision is made to proceed with a Cesarean delivery. All study subjects will have a 2nd IV cannula placed for drawing blood for study coagulation tests, and any other clinically indicated blood tests. The cannula will be connected to a stopcock with a "heparin lock" (cannula and stopcock are flushed with saline between aspirations) and left in place for 48 hours after delivery.